JP3902251B2 - Image forming apparatus and image forming method using the same - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus and an image forming method using the same, and more particularly to an image forming apparatus using a two-component developer and an image forming method using the same.
[0002]
[Prior art]
In general, the image forming apparatus includes an electrophotographic copying machine, a printer, a facsimile machine, and the like.
[0003]
One of the image forming methods used in the image forming apparatus is a method using a photoconductor as an image carrier. In this method, an electrostatic latent image is formed on a uniformly charged photoconductor by exposure or optical writing, and an image obtained by subjecting the electrostatic latent image to a visible image processing with a developer is recorded on a recording medium such as recording paper. To obtain a copy. As a developer used for visible image processing in this case, for example, a two-component developer in which a magnetic carrier and a toner are mixed is used.
[0004]
Ideally, all of the toner used in the visible image processing is transferred to the recording paper, but in reality, a part of the toner may remain on the photoreceptor.
[0005]
Conventionally, a cleaning process is provided to remove such residual toner. In this step, residual toner is mechanically scraped off using a blade or brush member that comes into contact with the surface of the photoreceptor.
[0006]
The toner scraped off from the photoconductor is currently stored in a recovery tank or the like and discarded. However, in recent years, resource saving has been demanded. Similarly, waste toner is also subject to recycling.
[0007]
Therefore, conventionally, the toner once removed from the photoreceptor in the cleaning process is reattached to the photoreceptor, and the toner is collected in a developing device used for visible image processing and reused. Proposed.
[0008]
As an example of a device having such a configuration,
(1) JP-A-5-61388
(2) Japanese Patent Publication No. 61-30274
(3) JP-A-6-51672
There is what is described in.
[0009]
In the configuration described in the gazette of (1), as shown in FIG. 28, an electrophotographic image is formed around the photosensitive drum 100 that is an image carrier along the rotation direction of the photosensitive drum 100 (the arrow direction in the drawing). A charging unit 101, an exposure unit 102, a plurality of developing units 103, an intermediate transfer drum 104, and a rotating brush 105 are arranged for executing the copying process, and the transfer unit 106 and the rotating brush are arranged on the outer periphery of the intermediate transfer drum 104. A recovery roller 107 in contact with 105 and a bias power source 108 connected to the recovery roller 107 are provided.
[0010]
The cleaning device having the above configuration corresponds to the rotating brush 105 and the bias power source 108.
[0011]
In the above configuration, the rotating brush 105 that can rotate in contact with the photosensitive drum 100 causes frictional charging by rotating in contact with the photosensitive drum, and scrapes by reversing the polarity of the residual toner on the photosensitive member. The removed and scraped toner is transferred by a bias power source 108 to a collecting roller 107 set to a polarity opposite to that of the toner. In particular, the material of the rotating brush 105 is selected so that the work function of the toner has a magnitude relationship with respect to the polarity of the toner that has been reversed at the time of scraping.
[0012]
In the configuration described in the publication (2), as shown in FIG. 29, a charging unit and an exposure unit for performing an electrophotographic copying process around the photosensitive drum 100 along the rotation direction of the photosensitive drum 100. And a latent image forming unit 110, a developing unit 111, a transfer unit 112, and a transfer roller 113, which are configured as described above. A bias power source 115 is connected to the transfer roller 113 via a changeover switch 114.
[0013]
The cleaning device having the above configuration corresponds to the bias power source 115 including the transfer roller 113 and the changeover switch 114.
[0014]
In the above configuration, the transfer roller 113 to which a bias voltage having a polarity opposite to the polarity of the toner remaining on the photosensitive drum 100 in one copying process is applied, removes the toner remaining on the photosensitive drum 100. By applying a bias voltage having a polarity opposite to the above bias voltage to a region of the surface of the photoconductive drum 100 that does not affect image formation on the surface of the photoconductive drum 100, the previously adsorbed toner is removed from the photoconductive body. The ink is reattached on the drum 100 and transferred to the developing unit.
[0015]
In the configuration described in the gazette of (3), although the configuration is not shown, a conductive member that comes into contact with the photosensitive member is provided, and the paper passing portion corresponding to the image forming area on the photosensitive member is in contact with the conductive member. In this case, the residual toner is adsorbed on the conductive member, and when the non-sheet passing portion corresponding to the non-image portion on the photosensitive member is in contact with the conductive member, the toner adsorbed on the conductive member is photosensitive. The toner is reattached on the body, transferred to a developing device, and the residual toner reattached on the photoconductor is collected by electrostatic force in the device.
[0016]
[Problems to be solved by the invention]
In any of the configurations described in the above publications, the toner remaining on the photosensitive member in the cleaning process is electrostatically adsorbed, and again adhered to the photosensitive member to transfer the toner toward the developing unit. The principle is to collect and reuse at the developing unit.
[0017]
However, the configurations described in these publications have the following problems.
[0018]
In general, the toner on the photoconductor that is transferred to the recording paper in the transfer process may reverse the polarity of the charge that has been held so far due to the transfer bias, so-called positive and negative polarity. There are many.
[0019]
For this reason, in the configurations described in the publications of (2) and (3), the toner adsorbed from the photosensitive member in the cleaning process is only one of the polarities, and the toner having the other polarity is on the photosensitive member. Still remains. For this reason, it is not expected to remove all toner from the photoreceptor.
[0020]
In addition, in the configuration described in the gazette of (2), since corona discharge and a lamp are used to carry out a static elimination process, which is one process of cleaning, there is a problem of generation of ozone in addition to a complicated structure. Invite.
[0021]
In contrast to the configuration described in each of the above publications, in the configuration described in the publication (1), the polarity adsorbed in the cleaning process is made uniform by frictional charging, but a fur brush is used as the configuration for that purpose. . For this reason, the contact probability between the toner and the brush is low. Accordingly, there is a problem that it is difficult to obtain a frictional force sufficient to reverse the polarity of the toner, and the residual toner cannot be completely recovered. Moreover, in addition to the fur brush, it is necessary to additionally provide a collecting member for collecting the toner adsorbed on the fur brush, so the structure cannot be denied.
[0022]
Ensure that the toner remaining on the photoreceptor during cleaning has a uniformly charged charge, and that a bias having a polarity opposite to that of the charged charge is applied, so that the residual toner is reliably sucked. In this case, however, the polarity of a part of the residual toner having a uniform charged charge may be reversed by being affected by the polarity of the bias. In particular, in the transfer process using a bias having a polarity opposite to the polarity of the developing bias applied in the developing device, the charged charge of the toner changes to the polarity of the transferring bias and becomes the same polarity as the bias used for suction. There is.
[0023]
For this reason, in order to reattach to the photoreceptor, the polarity of the bias is the same as the polarity of the charged charge of the toner during cleaning, and a high voltage necessary for transfer to the photoreceptor due to the repulsion of the toner is applied. Even in this case, the toner whose polarity is changed and has a polarity opposite to the bias polarity at the time of reattachment does not transfer onto the photosensitive member, but remains attached to the cleaning member as it is. There is a possibility that the recovery efficiency at the time of recovery may decrease.
[0024]
In addition, in this case, in order to transfer the residual toner adsorbed from the photoreceptor in the cleaning process including the toner having the changed polarity toward the photoreceptor by repulsion and reattach it, In order to make the polarity uniform, an appropriate charging method is required.
[0025]
Conventionally, friction charging has been used as a method for charging toner attracted and held by a cleaning member in a cleaning process so as to have a uniform polarity. This is because the photosensitive member and the cleaning member are brought into contact with each other, and the contacted region is used as a toner nip portion, and the photosensitive member and the cleaning member are moved at different velocities at the nip portion so as to be frictionally charged. It has become.
[0026]
However, in order to satisfactorily align the polarity by triboelectric charging, the nip portion becomes considerably large, which increases the size of the cleaning member, resulting in an increase in the size of the apparatus structure.
[0027]
In addition, when the nip portion of the cleaning member is enlarged, the area where the cleaning member adsorbs the residual toner is reduced, and the residual toner may not be successfully collected from the photoconductor. In addition, when the cleaning member is constituted by a roller, as the nip portion becomes larger, the adsorption area of the residual toner in the circumferential direction decreases, so that the toner adsorbed and held by the cleaning member becomes smaller in the nip portion. Probability of approaching the neighborhood increases. In this case, since the transfer bias used in the transfer process has a considerably high potential compared to the residual toner suction bias in the cleaning member, the toner on the cleaning member in the vicinity of the photosensitive member has the bias potential. The difference causes suction to the image area side of the photoreceptor and reverse transition.
[0028]
Therefore, when the toner is reversely transferred to the image area on the photosensitive member, the amount of the toner that is frictionally charged at the nip portion increases abnormally, which increases the load against the frictional charging, and the friction charging. Therefore, it is difficult to uniformly convert all the residual toner from the photosensitive member to the cleaning member.
[0029]
Further, when the toner adsorbed and held by the cleaning member from the surface of the photosensitive member is reattached to the photosensitive member again, the toner is in a region less than the moving direction length of the cleaning member regardless of the moving direction of the cleaning member relative to the photosensitive member. When this suction holding is performed, only that portion is always used for the suction holding and reattachment of toner. For this reason, for example, when the cleaning member is constituted by a roller, local contact is repeated in the circumferential direction, wear in that portion becomes remarkable, and cleaning characteristics due to toner adsorption holding and reattachment are exhibited. There is a possibility that it is impossible to collect all of the toner remaining after being lowered.
[0030]
Depending on the material, the photoconductor is charged under the influence of a bias voltage applied during the transfer process and during the cleaning process. Normally, such charging of the photoconductor is neutralized before the next image formation, but depending on the material of the photoconductor, there are cases where it cannot be eliminated. As a configuration for static elimination, photo neutralization using a lamp is performed based on the characteristics of the photoconductive layer used as a photoconductor, but the polarity of the charge for which neutralization by this light is effective is negative. However, in recent years, when an organic material such as OPC is used as the photoconductive layer, positive charges may remain, and in this case, photostatic discharge may not be performed. For this reason, the surface potential set in the next charging step is not uniform, and the potential of the electrostatic latent image changes, which may adversely affect the image density at the time of development.
[0031]
In the transfer process, which is one of the processes used in the image forming process, a conductive member that can come into contact with the photoconductor is used, and a transfer bias is applied to the photoconductor while holding and conveying the fed transfer paper. The upper image is electrostatically transferred onto the transfer paper. However, the conductive member used for such a transfer usually stops the transfer bias at the same time as the transfer paper is nipped and conveyed. However, in the vicinity of the rear end of the transfer paper, the photosensitive member and the conductive member are used. , The transfer bias affects the residual toner on the photoconductor, and the toner remaining on the photoconductor may be electrostatically attracted toward the surface of the conductive member. For this reason, the toner adhering to the surface of the conductive member may be transferred to the back surface of the transfer paper to be transported next, which may cause so-called stain on the transfer paper.
[0032]
Further, when collecting the toner remaining on the photosensitive member in the cleaning process, immediately after starting up the image forming apparatus or when performing initialization such as warming up, there is also some cause, for example, paper In some cases, after the apparatus stops before transfer due to clogging (jam) or the like, the photosensitive member is rotated again and cleaning is performed to initialize the photosensitive member.
[0033]
In the latter case, a considerable amount of toner is deposited on the photoreceptor, including toner carried for transfer. For this reason, even when toner is attracted by the cleaning member, the amount of toner is too large to be completely adsorbed, and a part of the toner may remain on the photoconductor. For this reason, for example, when a contact type charging device that contacts the photosensitive member is used as the charging device, residual toner enters between the charging device and the surface of the photosensitive member. Processing cannot be executed. If the uniform charging process is not performed, white stripes are generated on the photosensitive member, and a defective image is obtained.
[0034]
In order to eliminate this problem, it is conceivable to control the voltage in order to increase the strength of the electric field acting on the cleaning member, as described in the above publication (3). However, in such a case, the direction of the applied electric field is switched corresponding to the strength of the electric field that acts when the toner is attracted to the cleaning member and when the toner is reattached to the photosensitive member, and a relatively high static elimination potential. Is repeated, the electrostatic fatigue of the photoconductive layer on the photoconductor may become prominent and the life of the photoconductor may be shortened.
[0035]
In addition, the cleaning member used in the cleaning process has a function of removing toner remaining on the photosensitive member by contacting the photosensitive member, but is always in contact with the surface of the photosensitive member. In other words, when the photosensitive member is stopped, it is in contact with the same position on the surface of the photosensitive member. For this reason, when the cleaning roller is used as a cleaning member, the surface of the photosensitive member is deposited on the cleaning roller or the material constituting the photosensitive layer of the photosensitive member and the cleaning roller are used. A chemical reaction occurs with the contained components, and a part of the surface of the photoreceptor is transformed more than the other parts, so that an image is formed on a part of the image obtained at the next start of the photoreceptor. There was a problem that white streaks due to omission occurred.
[0036]
Further, when the photosensitive member is stopped, if the toner remains in the nip portion formed at the position facing the cleaning roller, the toner may change over time. In particular, under high-temperature and high-humidity environmental conditions, the toner is solidified, and it is easy to lose the elastic function, which is the characteristic of the cleaning roller, and the function of removing the toner from the surface of the photoreceptor may be lowered. was there.
[0037]
When the above-described cleaning failure occurs, in the charging process performed after the cleaning process, if the charging member is in contact with the photosensitive member and the charge is injected, residual toner adheres to the charging member. As a result, uniform charging cannot be performed.
[0038]
SUMMARY OF THE INVENTION Accordingly, a first object of the present invention is to provide an image forming apparatus having a simple configuration and capable of completely adsorbing all residual toner after transfer on an image carrier to a cleaning member.
[0039]
A second object of the present invention is to provide an image forming apparatus having a configuration capable of making a configuration for collecting all of the toner remaining on the image carrier without causing an increase in the size of the device. It is to provide.
[0040]
A third object of the present invention is to provide an image forming apparatus capable of improving the cleaning performance of residual toner on a photoconductor and recycling toner for collecting and reusing the residual toner on the photoconductor in a developing unit. There is.
[0041]
The fourth object of the present invention includes the initialization process of the image carrier, and after the image forming apparatus stops before reaching the cleaning process, it remains on the image carrier again when the apparatus is started or when warming up. An object of the present invention is to provide an image forming apparatus capable of preventing defective cleaning due to a large amount of toner and preventing the formation of a defective image and the deterioration of the life of an image carrier.
[0042]
A fifth object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of white stripes on an image.
[0043]
A sixth object of the present invention is an image forming apparatus capable of uniform charging by reliably removing residual toner in a nip formed between an image carrier such as a photoconductor and a cleaning member facing the image carrier. Is to provide.
[0044]
A seventh object of the present invention is to provide an image forming method capable of uniformly charging the next image formation.
[0045]
An eighth object of the present invention is to prevent transfer of toner from a transfer device that contacts a component used in an image forming process, particularly an image carrier, to transfer paper, thereby preventing the back of the transfer paper from being stained. It is to provide a forming method.
[0046]
A ninth object of the present invention is to provide an image forming method capable of collecting all of the toner remaining on the image carrier.
[0047]
[Means for Solving the Problems]
  In order to achieve this object, the invention described in claim 1An image carrier and a cleaning member made of a rotatable conductive roller arranged in a state of being pressed against the surface of the image carrier, and unidirectional during one image forming process for the image carrier The residual toner adhering to the surface of the image carrier by applying an electric field is adsorbed and held on the cleaning member, and then the direction of the electric field is switched to remove the adsorbed toner from the image carrier. In the above-described image forming apparatus, the toner is reattached to a region that does not affect the next image formation and transferred to the developing unit used in the image forming process, and the transferred toner is electrostatically collected in the developing unit. The cleaning member is disposed in contact with the image carrier.Rotate with a speed difference with the image carrier,Image carrierNip part withResidual toner adhering to the image carrier after transferTheRubbing and charging the toner to the same polarityMakeA cleaning roller; and a voltage applying unit that applies a voltage to the cleaning roller and causes the residual toner on the image carrier charged to the same polarity to be attracted to the cleaning roller. The cleaning roller includes the image carrier. When the friction application is carried out by rubbing the residual toner by forming a nip part at the contact part withThe toner of the same polarity and the opposite polarityWhen applying the voltage, the residual toner is sucked and when the sucked residual toner is returned to the image carrier, the polarity of the voltage applied by the voltage applying means can be switched.
[0048]
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, in addition to the voltage applying means provided in the cleaning member, the developing device used in the image forming process includes a voltage applying means, The voltage applying means provided in the cleaning member applies a voltage opposite to that collected by the cleaning roller when the toner collected and collected on the cleaning roller is reused, and adheres to the cleaning roller. The toner recovered in this manner is reattached to an area other than the area where the next image formation is performed on the image carrier, and the voltage applying means provided in the developing device is reattached to the image carrier. A voltage of an electrode capable of adsorbing the toner thus applied is applied to the developing device.
[0049]
According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, in addition to the voltage applying means provided in the cleaning member and the voltage applying means provided in the developing device, the image forming process is performed. The transfer device used has a voltage applying means, and the voltage applying means provided in the transfer device is in a direction opposite to the time when the toner collected by adhering to the cleaning roller is reused. By applying a voltage of 1 to the image carrier to charge the surface of the image carrier, the toner collected by adhering to the cleaning roller is collected on the image carrier other than the region where the next image formation is performed. In addition, the voltage applying means provided in the developing device applies the voltage of the electrode capable of adsorbing the toner reattached on the image carrier to the developing device. It is characterized by applying to the location.
[0051]
Claim4The invention described in the above is the image forming apparatus according to claim 1,The cleaning member first forms an electric field in a direction in which the residual toner can be sucked from the image carrier as a switching order of the electric field direction when the residual toner is reattached on the image carrier. The electric field in the direction in which the residual toner is transferred onto the image carrier is set in the order in which it is formed.It is a feature.
[0052]
Claim5The described invention is claimed.4In the described image forming apparatus,In the cleaning member, when the voltage of the electric field formed first is opposite to the polarity of the charged charge generated in the toner due to frictional charging caused by the contact between the cleaning member and the image carrier, and is sucked from the image carrier. Set to a voltage higher than the voltage used forIt is a feature.
[0055]
Claim6The invention described in the above is the image forming apparatus according to claim 1,The cleaning member is made of rubber having a hardness of Asuka C20 to 38 degrees, the pressing force against the image carrier is 3 g / cm or more, and the linear velocity ratio with the image carrier is less than 1. Set to move in the forward and forward directions of the image carrier.It is a feature.
[0056]
Claim7The invention described in the above is the image forming apparatus according to claim 1,The cleaning member is made of rubber whose hardness is set to 20 to 38 degrees asuka C, the pressing force against the image carrier is set to 3 g / cm or more, and the direction opposite to the moving direction of the image carrier To go toIt is a feature.
[0058]
Claim8The described invention is claimed.4In the described image forming apparatus,The cleaning member includes a plurality of voltage control means for applying a voltage capable of transferring the toner collected and adhered from the image carrier to the image carrier.
The plurality of voltage control means have different electric field strengths such that the toner held on the cleaning roller is directed toward the photoconductor.It is a feature.
[0059]
Claim9The described invention is claimed.8In the described image forming apparatus,In order to remove the toner on the photoconductor immediately after the power is turned on or during the warm-up, a voltage control unit is applied to form an electric field so that the developed toner is directed to the cleaning roller, and then the toner on the cleaning roller is transferred to the photoconductor. The voltage control means at that time forms a stronger electric field than the voltage control means during image formation.It is a feature.
[0060]
Claim10The described invention is claimed.8In the described image forming apparatus,After a certain period of time after image formation is stopped, the toner is reattached on the photosensitive member, and the voltage control means at that time forms a stronger electric field than the voltage control means during image formation.It is a feature.
[0061]
Claim1 1The described invention is claimed.8In the described image forming apparatus,Once a fixed number of sheets, the toner is reattached on the photosensitive member by a voltage control means of a strong electric field different from the normal one.It is a feature.
[0076]
[Action]
According to the first aspect of the invention, during recording, the cleaning roller rotates together with the image carrier, and after the transfer, the toner remaining on the image carrier is rubbed and charged to the same polarity. While electrostatically adsorbed by the cleaning member, voltage is simultaneously applied to the cleaning member by the voltage applying means, and residual toner on the image carrier charged to the same polarity is adsorbed by the cleaning member, and the surface of the image carrier is Clean it.
[0077]
According to the second aspect of the present invention, when the collected toner adsorbed by the cleaning member is reused, the voltage applying means applies a voltage having a polarity opposite to that at the time of adsorption to the cleaning member and adheres to the cleaning member. The toner is reattached to a region other than the region where the next image is formed, and the reattached toner is recovered by being directed back to the developing device side by a voltage of an adsorbable polarity applied to the developing device.
[0078]
According to the third aspect of the present invention, when the recovered toner adsorbed by the cleaning member is reused, the surface of the image carrier is charged by the transfer device, and the toner adsorbed by the cleaning member is subjected to the next image formation. The toner is reattached to a region other than the region, and the reattached toner is collected by being attracted and returned to the developing device side using the polarity of the voltage applied to the developing device.
[0079]
Claim 4And 5In the described invention, even if some of the residual toner sucked and held by the cleaning member adheres by reversing the polarity to the polarity opposite to the polarity necessary for suction holding, the direction of the applied electric field is By switching, the image is transferred onto the image carrier.
[0081]
Claim6In the described invention, even when the cleaning member moves in the forward direction and the moving direction of the image carrier, the critical hardness with the least wear of the image carrier can be obtained, and the criticality at which the frictional charging of the toner is most effectively performed. Pressure and rubbing speed are obtained.
[0082]
Claim7In the described invention, the cleaning member is moved in the direction opposite to the moving direction of the image carrier to obtain the rubbing state necessary for the frictional charging of the toner.
[0084]
Claim8In the described invention, the electric field strength can be optimally set by the plurality of voltage control means in accordance with the amount of toner adsorbed and held on the cleaning roller, and the toner can be reliably recycled on the photosensitive member. It can be attached and transferred to the developing unit and collected.
[0085]
Claim9In the described invention, the voltage control means for forming an electric field so that the developed toner is directed to the cleaning roller is operated, and then the toner on the cleaning roller is reattached on the photosensitive member, and the voltage control means at that time is made. Since the toner is reattached on the photosensitive member by the voltage control means having an electric field stronger than the voltage control means in the image, the toner is increased and held on the cleaning roller after the jam to remove the toner having a large M / A after development. All of the toner can be reattached on the photoreceptor, and can be transferred to the developing unit and collected.
[0086]
Claim10In the described invention, even when an abnormal amount of input toner is generated, for example, when an A3 transfer sheet is passed through an A3 document, all the increased toner is re-adhered on the photosensitive member. It can be transferred to the developing unit and collected.
[0087]
Claim11In the described invention, the transfer rate decreases due to the paper thickness, environment, etc., the amount of residual toner increases, and the toner on the cleaning roller increased by removing the toner can be re-adhered on the photosensitive member. It can be transferred to the department and collected.
[0099]
【Example】
Details of the present invention will be described below with reference to embodiments shown in the drawings.
[0100]
FIG. 1 is a schematic diagram illustrating a basic configuration of an image forming apparatus according to an embodiment of the present invention.
[0101]
In FIG. 1, an image forming apparatus 1 includes a photosensitive drum 2 as an image carrier. Hereinafter, the case where the image carrier is the photosensitive drum 2 will be described.
[0102]
The photosensitive drum 2 has a photosensitive layer made of an organic material such as OPC on its surface, and is provided so as to be rotatable in a direction indicated by an arrow by a driving device (not shown). A charging device 3, an exposure device 4, a developing device 5, a transfer device 6, a cleaning device 7, and a charge removal device 11 are arranged along the image forming process.
[0103]
The charging device 3 is provided so as to be able to come into contact with and separate from the photosensitive drum 2, and the configuration for that purpose is shown in FIG.
[0104]
In FIG. 2, the charging device 3 employs a method in which charges are injected by contacting the photosensitive drum 2. For this reason, the charging device 3 includes a charging roller 3A made of a conductive member that can come into contact with the surface of the photosensitive drum 2, and the charging roller 3A can be moved up and down with respect to a bracket 3B that can move up and down. Is rotatably supported by a rotating shaft 3A1 fitted in the. As a result, when the charging roller 3 </ b> A comes into contact with the photosensitive drum 2, the charging roller 3 </ b> A can be rotated with the rotation of the photosensitive drum 2. The rotating shaft 3A1 is usually given a habit of being able to move toward the photosensitive drum 2 by a coil spring 3C disposed between the bracket 3B and the support plate 3A2.
[0105]
The bracket 3B is formed of an angle piece, and the upper piece is fixed to the lifting shaft 3D.
[0106]
The elevating shaft 3D is a rod member in which a fixing portion of the bracket 3B is formed on a flat surface. The elevating shaft 3D moves the bracket 3B up and down with respect to the photosensitive drum 2 by raising and lowering the bracket 3B according to the elevating operation of the elevating drive piece 3E described later. Can be separated.
[0107]
The raising / lowering drive piece 3E is connected to the actuator 3F1 of the solenoid 3F. The solenoid 3F includes a coil spring 3F2 disposed between the main body and the actuator 3F1, and is normally maintained in a non-excited state, and in this state, the actuator 3F1 is lifted by the bias of the coil spring 3F2. Accordingly, during normal operation of the solenoid 3F, the charging roller 3A can move in a direction away from the photosensitive drum 2.
[0108]
The non-excited state of the solenoid 3F is set in a period other than the charging process. As a result, the charging roller 3A can contact the photosensitive drum 2 only during the charging step to uniformly charge the photosensitive layer of the photosensitive drum 2.
[0109]
In FIG. 1, the charging device 3 includes a power source 3G connected to the charging roller 3A. The power source 3G is provided with a circuit for applying a charging potential of −850 V to the charging roller 3A and a ground circuit. It has been. For each of these circuits, a switch 3H is provided so that a circuit capable of applying the charging potential when the charging roller 3A is in contact with the photosensitive drum 2 is connected.
[0110]
As the switch 3H, an electronic component such as a micro switch or a transistor that is operated manually or automatically by an actuator (not shown) is applied. The configuration of this switch is the same for the switches provided in each device described below.
[0111]
The exposure device 4 uses an optical writing format using laser light in accordance with an image writing signal from the image reading device, and forms an electrostatic latent image on the photosensitive layer of the photosensitive drum 2. As a configuration of the exposure apparatus 4, it is possible to use a format in which an original on the original table is exposed using an imaging optical system.
[0112]
As the developing device 5, a magnetic brush developing device is used. The magnetic brush developing device in this embodiment uses a two-component developer in which frictionally charged toner is magnetically adsorbed on a magnetic carrier. For this reason, the developing device 5 is provided with a developing sleeve 5B that can be rotated close to the surface of the photosensitive drum 2 and a stirring screw 5C for frictional charging of toner in the developing tank 5A.
[0113]
The developing sleeve 5 </ b> B is provided with a magnetic pole that forms a developing main pole disposed inside and opposed to the photosensitive drum 2, and a conveying magnetic pole for conveying the developer, and can carry a magnetic brush on the surface.
[0114]
The magnetic brush performs the visible image processing of the latent image by contacting the electrostatic latent image formed on the photosensitive drum 2 after the carrying amount on the surface of the developing sleeve 5B is regulated by the doctor member 5D. Can do.
[0115]
Connected to the developing sleeve 5B is a power source 5E for applying a developing bias for facilitating electrostatic adsorption of the toner in the developer carried on the surface to the electrostatic latent image on the photosensitive drum 2. . The power source 5E is provided with a circuit for applying a voltage of −600 V to the developing sleeve 5B and a circuit for applying a voltage of +150 V, and these circuits are switched by a switch 5F. Yes.
[0116]
The switching of the voltage to the developing sleeve 5B in the developing device 5 will be described in detail later during development, and the toner that remains on the photosensitive drum 2 and is reversed to the opposite polarity to that during development is sucked. It is supposed to be done with time. In the configuration shown in FIG. 1, a voltage of −600 V is selected during development, and a voltage of +150 V is selected during toner suction. As a result, during development, repulsive transfer of toner from the developing sleeve 5B toward the photosensitive drum 2 is easily performed, and during suction of toner, suction transfer of toner whose polarity is reversed is easily performed. .
[0117]
The transfer device 6 is composed of a semiconductive roller capable of contacting a photosensitive drum 2 by mixing a conductive material such as carbon in urethane rubber, and is connected to a power source 6A for applying a transfer bias. Yes.
[0118]
The power supply 6A includes a circuit that applies +950 V, which is a voltage as a transfer bias, a ground circuit, and a circuit that applies a voltage that is higher than the transfer bias potential (not shown). It can be switched.
[0119]
The transfer bias is applied when the visible image carried on the photosensitive drum 2 is electrostatically transferred to the transfer paper S fed from the paper supply device 8. A circuit for applying a voltage equal to or higher than the transfer bias potential is connected when a residual toner reattachment area on the photosensitive drum 2 faces.
[0120]
The reason for applying a voltage higher than the transfer bias is as follows.
That is, a part of the toner charged to the negative polarity by the developing bias in the developing device 5 remains in the vicinity of the rear end of the image forming area of the photosensitive drum 2, and the toner is half of the transferring device 6 by the transfer bias (+ 950V). This is because when the toner is attracted and adhered to the conductive roller and charged to the positive electrode, the toner is transferred to the re-attachment region of the photosensitive drum 2.
[0121]
The paper feeding device 8 includes a pair of registration rollers 8A for feeding the transfer paper S fed out from the paper feed cassette containing the transfer paper S in alignment with the image leading edge position on the photosensitive drum 2. Yes.
[0122]
The cleaning device 7 is provided so as to be able to come into contact with and separate from the photosensitive drum 2, and the configuration for that purpose is shown in FIG.
[0123]
In FIG. 3, the cleaning device 7 includes a cleaning roller 7 </ b> A supported so as to be able to come into contact with and separate from the photosensitive drum 2 by a contact / separation unit 70 described later.
[0124]
The cleaning roller 7A has a rotation shaft 7A1, and the rotation shaft 7A1 is slidably provided by a cleaning case 7B formed in a shape capable of exposing a part of the peripheral surface of the roller 7A. The support plate 7C is rotatably supported. The support plate 7C is given a habit of moving the cleaning roller 7A toward the photosensitive drum 2 by a coil spring 7D disposed between the support plate 7C and the cleaning case 7B.
[0125]
The cleaning roller 7 </ b> A is set in a rotational direction so that it can move in the same direction as the drum 2 at the contact position with the photosensitive drum 2 after contacting the photosensitive drum 2. Is set at a speed slightly higher than the peripheral speed of the photosensitive drum 2 and rubs residual toner adhering to the photosensitive drum 2. In the configuration shown in FIG. 1, the rotational speed of the cleaning roller 7 </ b> A is set to about 1.4 times the rotational speed of the photosensitive drum 2.
[0126]
As shown in FIG. 3, the cleaning case 7 </ b> B has a support shaft 7 </ b> B <b> 1 inserted through the upper piece, and can swing around the support shaft 7 </ b> B <b> 1 as a fulcrum.
The cleaning case 7B can swing in a direction in which the cleaning roller 7A is brought into contact with the photosensitive drum 2 and a direction in which the cleaning roller 7A is separated from the photosensitive drum 2. In order to separate the cleaning roller 7A from the photosensitive drum 2, a tension spring 7E is provided between the lower piece and the non-moving portion.
[0127]
The cleaning roller 7A is provided so as to be able to come into contact with and separate from the photosensitive drum 2. However, the contacting / separating means 70 for the cleaning roller 7A is provided for swinging the cleaning case 7B. It is constituted by.
[0128]
The swing drive unit 7F includes an eccentric cam 7F1, a cam shaft 7F2, a one-way rotation clutch 7F3, a solenoid 7F4, and a clutch lever 7F5.
[0129]
The eccentric cam 7F1 is fixed to the cam shaft 7F2, and the cam shaft 7F2 is connected to the one-way rotation clutch 7F3.
[0130]
The one-way rotation clutch 7F3 is formed with a locking projection 7F3A at a relative position of the trunk portion. One locking end of a clutch lever 7F5 that is connected to the actuator 7F4A of the solenoid 7F4 and can swing is opposed to the locking projection 7F3A.
[0131]
The one-way rotation clutch 7F3 stops the rotation of the cam shaft 7F2 when the large diameter portion of the eccentric cam 7F1 contacts the back surface of the cleaning case 7B and when the small diameter portion contacts the back surface of the cleaning case 7B. It has become. For this reason, the one-way rotation clutch 7F3 is provided with a locking projection 7F3A provided on the body portion with a phase of 180 degrees.
[0132]
The solenoid 7F4 is driven and controlled by a control unit (not shown), and is maintained in a state in which the actuator 7F4A protrudes as a non-excited state corresponding to a normal time. For this reason, the clutch lever 7F5 swings counterclockwise in the drawing and can be engaged with the locking projection 7F3A of the one-way rotary clutch 7F3. When the solenoid 7F4 is excited, the contact relationship between the eccentric cam 7F1 and the cleaning case 7B is changed.
[0133]
When the large diameter portion of the eccentric cam 7F1 contacts the back surface of the cleaning case 7B, the cleaning roller 7A contacts the surface of the photosensitive drum 2, and when the small diameter portion of the eccentric cam 7F1 contacts the back surface of the cleaning case 7B. The cleaning roller 7A can be separated from the surface of the photosensitive drum 2.
[0134]
In FIG. 1, a cleaning power supply 7G is connected to the cleaning roller 7A.
[0135]
The cleaning power supply 7G is provided with circuits for applying +300 V and −500 V and +500 V (not shown), and these circuits are connected to the cleaning roller 7A via a switch 7H. Each of these circuits is provided to form an electric field that contributes to toner transfer.
[0136]
The circuit for applying +300 V is selected when an electric field for attracting the toner remaining on the photosensitive drum 2 is formed. The circuit for applying -500 V and +500 V is selected by the cleaning roller 7A. 2 is selected when an electric field for transferring the attracted residual toner toward the photosensitive drum 2 is formed at the time when the suction of the residual toner existing in the image forming area on the image 2 is completed.
Such switching of the bias voltage is for the following reason.
[0137]
The toner charged on the negative electrode by the developing bias adheres to the image on the photosensitive drum 2 subjected to the visible image processing by the developing device 5.
[0138]
The toner in the image when transferred to the transfer paper S in the transfer process is charged positively by the transfer bias. For this reason, the toner remaining on the photosensitive drum 2 after the transfer process is a mixture of positive and negative polarity toners. FIG. 4 shows this state.
[0139]
On the other hand, as shown in FIG. 5, the toner that contacts the cleaning roller 7A after the transfer process is rubbed at the nip portion corresponding to the contact position between the cleaning roller 7A and the photosensitive drum 2 due to the difference in peripheral speed between the two. Charged. As shown in FIG. 5, the polarity generated by frictional charging is all set to the negative electrode. For this reason, the residual toner turned to the negative electrode is transferred in the direction attracted by the electric field in one direction formed by the voltage of +300 V, which is the voltage from the power supply circuit 7G applied to the cleaning roller 7A, and the photoreceptor. The drum 2 is removed. As the material of the cleaning roller 7A, a material having conductivity capable of applying a bias voltage and capable of setting the polarity of the toner to the negative electrode by frictional charging is selected.
[0140]
On the other hand, the toner transferred onto the cleaning roller 7A has a voltage of −500 V, which is a voltage from the power supply circuit 7G applied to the cleaning roller 7A when the image forming area on the photosensitive drum 2 has passed through the cleaning roller 7A. The electric field in the other direction formed by the voltage repels the surface of the cleaning roller 7 </ b> A and reattaches to the surface of the photosensitive drum 2.
[0141]
The toner re-adhered on the photosensitive drum 2 is attracted by the rotation of the photosensitive drum 2 when the polarity of the developing bias is switched to the positive polarity when facing the developing sleeve 5B in the developing device 5. To be recovered.
[0142]
In the configuration shown in FIG. 1, the toner remaining on the photosensitive drum 2 is removed and the toner is collected by the developing device 5 by bias control in the cleaning device 7.
[0143]
In FIG. 1, reference numeral 9 denotes a static elimination needle that neutralizes the charge remaining on the transfer paper S, reference numeral 10 denotes a transport device for transporting the transfer paper S toward a fixing device (not shown), and Reference numeral 11 denotes a static eliminator constituted by a lamp that is lit while the photosensitive drum 2 is moving.
[0144]
Examples of the invention described in each claim will be described below.
[0145]
FIG. 6 is a timing chart for explaining an embodiment of the present invention. In the image forming process described below, a case where a positive image is formed from a negative image is targeted.
1 and 6, when a print button is turned on (ON) in an operation unit (not shown) to start image formation, the photosensitive drum 2 starts to rotate. At this time, in the charging device 3, the charging roller 3 </ b> A comes into contact with the photosensitive drum 2 when the solenoid 3 </ b> F is excited, and the switch 3 </ b> H is switched by the power source 3 </ b> G, so that the negative voltage of “−850 V” is uniform. Charging is performed.
[0146]
The uniformly charged photoconductive drum 2 is subjected to optical writing by the exposure device 4 after the charging step to form an electrostatic latent image. In the latent image, the surface potential of the photosensitive drum 2 at a position corresponding to the black solid image is “−150 V”.
[0147]
The surface of the photosensitive drum 2 on which the electrostatic latent image is formed faces the developing sleeve 5B of the developing device 5, and the visible image processing of the electrostatic latent image is performed. At this time, in the developing device 5, a developing bias of “−600 V” is applied from the power source 5E to the developing sleeve 5B. Therefore, the toner in the developer carried on the developing sleeve 5B is transferred toward the electrostatic latent image, and the electrostatic latent image can be visualized.
[0148]
The photosensitive drum 2 carrying a visible image in which the electrostatic latent image is visualized faces the transfer device 6.
[0149]
In the transfer device 6, a transfer bias of “+950 V” is applied from the power source 6 </ b> A, whereby the toner in the visible image carried on the photosensitive drum 2 is transferred to the transfer paper S fed out from the paper supply device 8. Is attracted by suction.
[0150]
The transfer sheet S is peeled off from the photosensitive drum 2 and conveyed to a fixing device (not shown) by the conveying device 10, and the transferred toner is heated and fused in the fixing device.
[0151]
After the transfer process, the photosensitive drum 2 moves toward the cleaning device 7 and a cleaning process is performed in which the toner remaining in the image area on the photosensitive drum 2 is sucked and collected by the developing device 5. Residual toner that has not been transferred in the transfer process is present on the surface.
[0152]
As described with reference to FIG. 4, the residual toner includes both positive and negative polarities depending on the applied transfer bias. In practice, the residual toner is charged to the positive electrode due to the difference between the transfer bias and the development bias. The amount of residual toner is extremely large.
[0153]
In the cleaning device 7, the cleaning roller 7 </ b> A is moved to the photosensitive drum 2 from the time when the print button is turned on, including the time when image formation on the first image area corresponding to the image forming area on the photosensitive drum 2 is started. It is made to contact | abut on the surface of.
[0154]
Note that the charging device 3 is separated from the surface of the photosensitive drum 2 when the trailing edge of the image area ends the charging process, and the charging potential on the photosensitive drum 2 is set to “0V”.
[0155]
The contact operation of the cleaning roller 7A is performed by switching the excitation state of the solenoid 7F4 provided in the contact / separation means 70 described in FIG.
When the excitation state of the solenoid 7F is switched, a state is set in which the large diameter portion of the eccentric cam 7F1 is in contact with the back surface of the cleaning case 7B. As a result, the contact area between the surface of the photosensitive drum 2 and the cleaning roller 7A constitutes a nip portion, and residual toner is frictionally charged in the nip portion to charge the negative electrode. At this time, a voltage of “+300 V” is applied from the power supply 7G to the cleaning roller 7A, and the residual toner that has turned to the negative electrode due to frictional charging can be attracted to the cleaning roller 7A.
[0156]
On the other hand, the cleaning roller 7A that sucks the residual toner at the rear end of the image area from above the photosensitive drum 2 is applied by the developing device 5 from the applied voltage from the power source 7G “+300 V” for sucking the toner. The polarity of the developing bias is switched to “−500 V” of the negative electrode, and the direction of the electric field between the photosensitive drum 2 and the cleaning roller 7A is changed.
[0157]
During the voltage switching period to “−500 V” with respect to the cleaning roller 7A, the rear end of the first image area of the photosensitive drum 2 by the cleaning roller 7A passes and the area from the leading end of the next image area passes. It corresponds to the period to do. As a result, the toner sucked by the cleaning roller 7 </ b> A repels and reattaches to the surface of the photosensitive drum 2 with respect to an area not related to image formation.
[0158]
The photosensitive drum 2 in which the toner remaining in the first image area is attracted by the cleaning roller 7A passes through the cleaning device 7 and is set to a surface potential of “0 V” by the static eliminator 11. However, since the charging device 3 is set in a state where it is separated from the photosensitive drum 2 and no voltage is applied from the power source 3G, the charging device 3 moves toward the developing device 5 without performing the charging process. To do.
[0159]
The surface potential of the photosensitive drum 2 is set to “0 V” when the rear end of the first image area on the photosensitive drum 2 passes through the charging device 3. Under the influence of the applied voltage from 7A, it is charged to “+ 20V” after the transfer and to “−50V” after the cleaning process. However, since the surface potential on the photosensitive drum 2 is reduced by removing the surface potential when the photosensitive drum 2 passes through the static eliminator 11, static electricity between the photosensitive drum 2 and the toner is removed. Electrical relationships are excluded.
[0160]
In the developing device 5, the applied voltage from the power source 5E is switched when the rear end of the first image area on the photosensitive drum 2 passes the developing sleeve 5B. The applied voltage is switched from “−600 V” functioning as a developing bias to “+150 V”.
[0161]
In the developing device 5, the polarity of the voltage applied to the developing sleeve 5 </ b> B is reversed from that at the time of development, so that the polarity is opposite to the polarity of the toner carried and transported on the photosensitive drum 2. Thus, the residual toner on the photosensitive drum 2 is transferred to the developing sleeve 5B and collected.
[0162]
The cleaning roller 7 </ b> A in the cleaning device 7 corresponds to a moving amount capable of reattaching toner onto the photosensitive drum 2 from the time when the rear end of the first image area on the photosensitive drum 2 passes. It rotates until it reaches rotation, and after one rotation, it is separated from the photosensitive drum 2. As a result, the background stain can be prevented by preventing the reverse transfer of the toner to the image area on the photosensitive drum 2.
[0163]
Since the photosensitive drum 2 that has passed through the developing device 5 faces the cleaning device 7 but is not in contact with the cleaning roller 7A, the remaining surface potential is removed by the charge removing device 11 as it is, and the next charging step is performed. Provided.
[0164]
FIG. 7 shows a timing chart when the above-described residual toner collecting step is executed while a plurality of transfer sheets are fed. In FIG. 7, the toner recovery during the feeding of a plurality of transfer sheets is the same as the process performed for the first sheet, but after the residual toner is adsorbed and held from the photosensitive drum 2. The rotation speed at the time of reattachment is not set to less than 1 in the above-described linear speed ratio, but is set to 1 or more, so that a paper feeding process period (in the drawing, The time required to reattach the toner to the photosensitive drum 2 in the sheet interval) can be shortened, so that the time until the second image is formed can be shortened.
[0165]
Next, claim 4And 5Examples of the described invention will be described.
[0166]
In the configuration described above, the toner sucked by the cleaning roller 7A may be reversed to the positive electrode even by frictional charging at the nip portion due to the influence of the transfer bias. Even when the negative voltage is applied, it remains adhered on the cleaning roller 7A.
[0167]
Therefore, in order to deal with such a case, a voltage of +500 V, which is the same polarity as the bias voltage used for suction of the toner that is frictionally charged in the nip portion and is higher than the voltage, is used. Thus, the toner charged on the positive electrode is transferred to the reattachment region of the photosensitive drum 2.
[0168]
Therefore, the cleaning roller 7A makes two rotations when facing the toner reattachment region corresponding to the region that does not affect the next image formation region, with the rear end of the image formation region of the photosensitive drum 2 as the start position. In the first rotation, the toner charged on the positive electrode of the polarity voltage capable of attracting the toner from the photosensitive drum 2 is rebounded and reattached to the photosensitive drum 2. An electric field is generated by applying a voltage (+500 V) that can be generated, and at the next rotation, the toner having the same polarity as that of the toner by triboelectric charging and held by suction is repulsively transferred toward the photosensitive drum 2 to re-apply. An electric field is formed by applying a voltage (−500 V) that can be adhered.
[0169]
Since the present embodiment is configured as described above, its operation will be described as follows based on the configuration shown in FIG. 1 and the timing charts shown in FIGS. In the image forming process described below, a case where a positive image is formed from a negative document is targeted.
[0170]
The basic operation for collecting the toner from the photosensitive drum 2 is the same as that of the first to third embodiments.
[0171]
This embodiment is characterized by the following points.
When the residual toner is sucked from the photosensitive drum 2 toward the cleaning roller 7A and is reattached toward the photosensitive drum 2, the polarity of the voltage applied to the cleaning roller 7A is important. Although the applied residual toner is frictionally charged at the nip portion shown in FIG. 5 and becomes negative, a part of the residual toner may be reversed depending on the polarity of the bias voltage at the time of transfer. The toner on the cleaning roller 7A reversed to the positive electrode remains attached on the cleaning roller 7A due to the influence of “−500 V” which is a negative bias voltage applied to the cleaning roller 7A when it is reattached to the photosensitive drum 2. Become.
[0172]
Therefore, the present embodiment is characterized in that all the toner sucked on the cleaning roller 7A including the toner having the reversed polarity is reattached to the photosensitive drum 2.
[0173]
FIG. 8 is a timing chart showing an embodiment in which the toner having the reverse polarity described above with respect to the basic operation shown in FIGS. 6 and 7 is reattached to the photosensitive drum 2 from the cleaning roller 7A. is there.
[0174]
In FIG. 8, the cleaning roller 7 </ b> A rotates twice when facing the reattachment region on the photosensitive drum 2, and “+300 V” that is a bias voltage for attracting toner from the photosensitive drum 2 at the first rotation. A higher voltage of “+500 V” is applied, and during the second rotation, a voltage of “−500 V” in which the polarity is reversed from the bias voltage for attracting toner is applied. As described above, the voltage applied first is made to correspond to a voltage having the same polarity as and higher than the bias voltage used for suction of the frictionally charged toner at the nip portion.
[0175]
The polarity is switched by re-adhering the toner reversed to the positive electrode among the toner sucked and held by the cleaning roller 7A toward the photosensitive drum 2 and then removing the toner having the negative electrode. The order of reattachment to the drum 2 is set.
[0176]
On the other hand, in the developing device 5, in order to cope with the case where the toner reversed to the positive electrode is reattached to the photosensitive drum 2 with respect to the bias voltage applied at the time of normal recovery, the timing is shown by a one-dot chain line in the drawing. A voltage lower than “+150 V”, which is a positive electrode bias voltage applied when collecting toner having a negative electrode, is set, and the voltage is inverted to the positive electrode due to the difference between this voltage and the bias voltage on the cleaning roller 7A side. A state is set in which the existing toner is likely to transfer toward the developing device 5 side. As described above, the toner that has been reversed to the positive electrode is first reattached on the photosensitive drum 2 and collected by the developing device 5 to ensure the time required for polarity change when frictionally charged in the developing device 5. It is to do.
[0177]
In the developing device 5 that has finished collecting the toner inverted to the positive electrode, the bias voltage is switched to “+150 V” that enables the toner charged on the negative electrode to be collected, and is reattached on the photosensitive drum 2. This makes it possible to collect the toner.
[0178]
In the above-described embodiment, the photosensitive drum 2 is charged by applying a bias voltage during the transfer process and the cleaning process. Specifically, “−20V” is charged after the transfer process, and “+ 50V” is charged after the cleaning process. Since the static eliminator 11 used in this embodiment is an optical static elimination method, when an organic material such as OPC is used as the material of the photosensitive drum 2, it is effective only for negative charge. Accordingly, it is necessary to reverse the polarity of the surface potential of the photosensitive drum 2 charged to the positive electrode to the negative electrode, or to reduce the surface potential to a surface potential that is easy to remove even the negative electrode.
[0179]
FIG. 9 and FIG. 10 show an embodiment in this case. In FIG. 9, after the toner is reattached in the process of moving the photosensitive drum 2, the toner is recovered by the developing device 5. In the transfer device 6 facing the photosensitive drum 2, the polarity of the surface potential of the photosensitive drum 2 is reversed to the negative electrode for charging.
[0180]
In FIG. 10, when the toner reattached to the photosensitive drum 2 is collected by the developing device 5 and then faces the cleaning device 7, the polarity of the surface potential is reversed to the negative electrode and charged by the cleaning device 7. Yes.
[0181]
When the polarity of the photosensitive drum 2 is set to the negative polarity by the transfer device 6 or the cleaning device 7, the surface potential is set to “0 V” by the photostatic discharge when facing the static eliminator 11, and it is uniform in the next charging process. Charging can be made possible.
[0182]
According to the present embodiment, it is possible to reduce the time required for the charge removal process in the image forming process by reducing the burden of the charge removal process performed by the charge removal apparatus.
[0183]
In this embodiment, when the cleaning device 7 sucks and holds the residual toner from the photosensitive drum 2 and reattaches it to the photosensitive drum 2, the transfer device is cleaned using the same technique. It has become.
[0184]
The transfer device 6 is in contact with the photosensitive drum 2 except when the transfer paper S is held and conveyed. Therefore, the vicinity of the rear end of the image area on the photosensitive drum 2 is affected by the transfer bias from the semiconductive roller of the transfer device 6 that is close to this position. Accordingly, when toner that has not been collected by the developing device 5 is present on the photosensitive drum 2, the toner is transferred and adhered to the transfer device 6 by the transfer bias, and this adhered toner is then nipped and conveyed. The transfer paper S may be transferred to the back surface of the transfer paper S, and so-called back soiling of the transfer paper S may be caused.
[0185]
Therefore, in this embodiment, by performing bias control on the transfer roller constituting the transfer device 6, the toner attached to the roller surface is reattached to the photosensitive drum 2 and self-cleaning can be performed by the transfer device 6. It is like that.
[0186]
FIG. 11 is a timing chart showing an embodiment in this case. In FIG. 11, when the region where the toner is reattached on the photosensitive drum 2 faces the transfer roller, the transfer device 7 includes the cleaning device 7. The reversal switching of the electric field direction is executed between the redeposition regions by the same procedure as the reversal switching of the electric field direction. As a result, regardless of the polarity of the toner adhering to the surface of the transfer roller, all the adhering toner can be adhered to the toner reattachment region on the photosensitive drum 2.
[0187]
The configuration of the charging device 3 is not limited to the contact type shown in FIG. 1, and it is possible to adopt a configuration in which charging can be performed by contacting a corona discharge method or a needle-like electrode as shown in FIG. Further, the cleaning device 7 is not detachable, and the cleaning roller can be provided in an immovable state by providing a gap on the surface of the photosensitive drum 2 that can contact the toner and allow charge injection. It is. In addition, the bias voltage and polarity are not limited to change the direction of the electric field by switching the polarity of the bias potential to the cleaning roller, and the direction of the electric field is switched by setting the polarity and surface potential on the photoconductor side. May be.
[0188]
Next claim6 and 7Examples of the described invention will be described.
[0189]
In FIG. 1, a cleaning roller 7A included in the cleaning device 7 is composed of a conductive elastic member made of rubber whose Asuka C is set to 20 to 38 degrees, preferably 38 degrees, and the pressing force against the photosensitive drum 2 is 3 g. It is set to / cm so that the photosensitive drum 2 rotates in the forward direction and the forward direction.
[0190]
Of these characteristics of the cleaning roller 7A, the pressing force against the photosensitive drum 2 is sufficient for friction charging even if the nip area is reduced, as shown in FIG. 13, and is applied to the cleaning roller 7A. Is a critical value that can be triboelectrically charged to a polarity so that the most toner can be attracted by the bias potential, and the hardness is a critical value that suppresses wear of the photosensitive drum 2 due to the pressure as shown in FIG. It is. As a result, even when a small nip region is set without promoting the wear of the photosensitive drum 2, the uniform polarity can be set for the residual toner to be sucked, and the transfer of the toner to the cleaning roller 7A side can be satisfactorily performed. Can be made to do.
[0191]
The cleaning roller 7 </ b> A is set in a rotational direction in which the cleaning roller 7 </ b> A abuts on the photosensitive drum 2 and can move in the same direction as the drum 2 at the contact position with the photosensitive drum 2. The linear speed ratio is set to a speed less than 1 with respect to the peripheral speed of the body drum 2. Accordingly, the cleaning roller 7A that moves in the forward direction with respect to the moving direction of the photosensitive drum 2, that is, the rotating cleaning roller 7A, can perform good rubbing when moved in the same direction at the nip portion. The toner is efficiently triboelectrically charged at the nip formed between the two. Therefore, in the nip portion, all of the toner remaining on the photosensitive drum 2 can be frictionally charged to the same polarity, in this case, the negative electrode. In addition, the cleaning roller 7 </ b> A is set to suck the toner remaining in the image area of the photosensitive drum 2 in an area less than the circumference. Thereby, the toner once sucked and held by the cleaning roller 7A does not again face the image area of the photosensitive drum 2.
[0192]
In such a configuration, the cleaning device 7 can obtain the same operation as that shown in FIGS. 6 and 7, but image formation on the first image area corresponding to the image formation area on the photosensitive drum 2. The cleaning roller 7A is in contact with the surface of the photosensitive drum 2 from the time when the print button is turned on including the time when the printing button is turned on, and the pressing force of the cleaning roller 7A against the photosensitive drum 2 in this case is Since the cleaning roller 7A rotates in the same forward direction as the rotation direction of the photosensitive drum 2, as described above, it is 3 g / cm, and the linear velocity ratio is set to be less than 1. Also, because the length of the image area along the rotation direction of the photosensitive drum 2 is set to be less than the circumferential length of the cleaning roller 7A, it is temporarily cut. Toner is adsorbed over training roller 7A, again, it never reaches the position facing the image area of the photosensitive drum 2. Accordingly, the rear end of the image area of the photosensitive drum 2 from which the residual toner is sucked by the cleaning roller 7A does not face the toner attracted and held by the cleaning roller 7A. Therefore, it is not affected by the charged charge in the image area, and thus no reverse transition to the image area of the photosensitive drum 2 occurs.
[0193]
Incidentally, the cleaning roller 7A for sucking the toner remaining in the image area on the photosensitive drum 2 can have the following relationship between the circumference and the image area.
[0194]
In the above embodiment, the toner remaining in the image area is sucked in the area less than the circumferential length of the cleaning roller 7A. However, when the circumferential length is simply used as a reference, the photosensitive drum 2 is used. The length of the image area along the rotation direction must be changed in accordance with the length of the electrostatic latent image forming area along the rotation direction of the photosensitive drum 2, which is an area used for transfer. For this reason, in this embodiment, the circumferential length of the cleaning roller 7A is set to a length that can include the length of the maximum image area in the image area. As a result, when the residual toner is suctioned for an image area that does not reach the maximum length of the image area, all the residual toner is sucked and sucked without having to rotate the cleaning roller 7A once. There is no reverse transfer of toner to the image area.
[0195]
Further, the rotation amount of the cleaning roller 7A with respect to the rotation speed of the photosensitive drum 2 may be changed in order to suck the residual toner from the image area of the photosensitive drum 2 in accordance with the length of the electrostatic latent image forming area. it can. In this case, the size of the transfer paper is detected, the size of the transfer paper, in particular, the length of the transfer paper along the rotation direction of the photosensitive drum 2, and the rotation of the cleaning roller 7A according to the detection result. What is necessary is just to change speed and control rotation amount. Accordingly, when the residual toner is sucked from the image area by the cleaning roller 7A for all the image areas that do not reach the length from the length of the maximum image area, the cleaning roller regardless of the length of the image area. Residual toner from the image area can be sucked with a circumference less than 7A, particularly less than one round, and a situation in which the sucked toner is reversely transferred to the image area is prevented.
[0196]
The frictional charging at the nip portion can also be performed by changing the rotation directions of the photosensitive drum 2 and the cleaning roller 7A in the above-described embodiment.
[0197]
In this case, the cleaning roller 7A is composed of a rubber having a hardness of 38 degrees to minimize the wear amount of the photoreceptor, as shown in FIG. The pressing force against 2 is set to 3 g / cm. The reason for this setting condition is the same as in the above embodiment.
[0198]
The rotational speed of the cleaning roller 7A relative to the rotational speed of the photosensitive drum 2 is not limited to be less than 1 in the linear speed ratio, and is set to an equal ratio, and the rotational direction of the cleaning roller 7A is a position facing the photosensitive drum 2. The rotation direction is set to be opposite to the moving direction of the photosensitive drum 2 in the nip portion.
[0199]
According to such a configuration, since the photosensitive drum 2 and the cleaning roller 7A move in opposite directions, the degree of rubbing at the nip portion is increased, and the toner can be efficiently charged by friction. When the length of the image area is extremely short with respect to the circumferential length of the cleaning roller 7A, the rotational speed is increased by setting the linear speed ratio to 1 or more, and the degree of rubbing at the nip portion is increased to increase the friction. You may make it improve charging efficiency. Even in this case, it is a matter of course that the toner remaining in the image area of the photosensitive drum 2 is sucked in an area less than the circumferential length of the cleaning roller 7A.
[0200]
According to such an embodiment, even when the nip region is small, it is possible to satisfy the conditions necessary for tribocharging, particularly the conditions for uniformizing the polarity of the residual toner.
[0201]
Further, the suction of the residual toner from the image area of the photosensitive drum 2 is performed in an area that is less than the circumferential length of the cleaning roller 7A. Therefore, the sucked toner does not reach the image area again, and does not reach the image area. It is not affected by the remaining bias potential. This prevents a situation in which the toner sucked toward the image area of the photosensitive drum 2 is reversely transferred.
[0202]
Incidentally, in the above-described embodiment, the rotation direction of the photosensitive drum 2 and the rotation direction of the cleaning roller 7A in the cleaning device 7 are set to the forward direction.
[0203]
In this case, as shown in FIG. 4, the polarity of the toner remaining on the photosensitive drum 2 after the transfer is uniform due to the frictional charging due to the peripheral speed difference between the cleaning roller 7A and the photosensitive drum 2. However, it is not always charged so that all the polarity of the remaining toner is uniform, and there is a tendency of the polarity of the remaining toner as a whole. The current situation is uniform. For this reason, the residual toner includes a toner having a polarity opposite to that due to frictional charging and a toner having no polarity (hereinafter referred to as a non-friction toner). Accordingly, the residual toner on the photosensitive drum 2 is mechanically scraped off at the nip portion by the cleaning roller 7A, but the toner having the opposite polarity or the non-friction toner is acting on the gap at the nip portion. As a result, reverse transfer to the photosensitive drum 2 may occur, which may cause a cleaning failure.
[0204]
Such a defect is caused by the rotational direction of the photosensitive drum 2 and the cleaning roller 7A, and the toner scraped from the surface of the photosensitive drum 2 to the cleaning roller 7A side is in the same direction as the movement of the photosensitive drum 2. This is because it moves and remains opposite the surface of the photosensitive drum 2.
[0205]
Therefore, the rotation direction of the cleaning roller 7A is set in a direction in which the photosensitive drum 2 moves in the relative direction at the nip portion. As a result, as shown in FIG. 5, the surface of the photosensitive drum 2 from which the residual toner is scraped to the cleaning roller 7A side does not face the toner adsorbed and held on the cleaning roller 7A side. The residual toner adsorbed and held on the photosensitive drum 2 is not transferred back to the photosensitive drum 2.
[0206]
However, when the rotation direction of the cleaning roller 7A is set and the adsorption and holding of the residual toner and the reattachment to the photosensitive drum 2 are repeated at a length equal to or less than the circumferential length of the cleaning roller 7A. In some cases, a part of the residual toner to be attracted and held from the photosensitive drum 2 remains and cannot be completely recovered. The reason will be described below.
[0207]
FIG. 16 is a schematic diagram in the case where toner is adsorbed and held and reattached in a region having a length less than the circumferential length of the cleaning roller 7A.
[0208]
In FIG. 16, a case where a region of 1/3 of the circumferential length is set as the region of the cleaning roller 7A for attracting and holding the residual toner from the photosensitive drum 2 will be described. When the toner that rotates in the reverse direction (the direction indicated by the symbol CW in the drawing) and remains on the surface of the photosensitive drum 2 is suction-held, a suction-holding bias is applied.
[0209]
In this case, the bias polarity is a (+) pole. As a result, the toner T1 remaining on the photosensitive drum 2 is, as shown in FIGS. 16A and 16B, regions in the circumferential direction indicated by reference numerals P1 and P0 (regions indicated by hatching in the drawing). And is held on the cleaning roller 7A (toner in a state indicated by symbol T2 in the drawing).
[0210]
When the toner adsorbed and held on the photosensitive drum 2 is reattached, the cleaning roller 7A rotates in the forward direction (the direction indicated by the symbol CCW in the drawing) with respect to the rotation direction of the photosensitive drum 2. Therefore, as shown in FIG. 16C, the toner that is attracted and held by the peripheral portions P1 and P0 of the cleaning roller 7A is applied with a polarity bias that can repel from the cleaning roller 7A side. It will reattach to the photosensitive drum 2.
[0211]
The facing position on the cleaning roller 7A after the reattachment of the toner to the photosensitive drum 2 is a position indicated by reference sign P0, which is the initially facing position of the circumferential portions P1 and P0. In this state, when cleaning is started again, the range from the position P0 to P1 is used for adsorbing and holding the toner. For this reason, the same area of the circumferential length portion of the cleaning roller 7A is in contact with the photosensitive drum 2 and this causes local wear in the circumferential direction of the cleaning roller 7A to be noticeable, and the cleaning efficiency tends to be lowered. Become.
[0212]
Therefore, in this embodiment, as shown in FIG. 15, the rotation amount of the cleaning roller is made different between when the toner is adsorbed and held and when it is reattached.
[0213]
In FIG. 15, the rotation of the cleaning roller 7A is the same as that shown in FIG.
[0214]
Initially, the position of the cleaning roller 7A facing the photosensitive drum 2 at the circumferential portion is set to the position indicated by the symbol P0 ′ (see FIG. 15A).
[0215]
In the case where the residual toner is attracted and held from the photosensitive drum 2, the peripheral portion of the cleaning roller 7A indicated by reference numerals P0 'and P1' in FIG. 15B is opposed to the photosensitive drum 2 to attract and retain the residual toner. (Toner in the state indicated by T2 in the figure).
[0216]
When the attracted and held toner is reattached to the photosensitive drum 2, as shown in FIG. 15C, the peripheral length portion longer than the length of the peripheral length portions (P 0 ′ to P 1 ′) when the toner is attracted and held is obtained. The position P2 corresponding to the obtained position moves until it faces the photosensitive drum 2.
[0217]
Next, at the time of the next toner adsorption holding, as shown in FIG. 15D, the length corresponding to the length of the initial peripheral portion (P0 ′ to P1 ′) is moved from the position P2 (P0 ′ to P1 ′). = P2-P3). As a result, the toner collection start position of the cleaning roller 7A facing the photosensitive drum 2 is sequentially shifted, so that the local facing relationship at the cleaning roller 7A is not maintained, and local wear is suppressed. Will be.
[0218]
According to such a configuration, the wear state in the circumferential direction of the cleaning roller 7A is made uniform, and the wear does not become conspicuous locally, so that the cleaning roller life is extended and the cleaning effect is stabilized. Can be made.
[0219]
Next, embodiments of the invention described in claims 12 to 15 will be described.
[0220]
In this embodiment, it is possible to clean residual toner when image formation is resumed after image formation is interrupted.
[0221]
The case where normal image formation is performed has been described. Next, the reverse transfer process in the case of abnormality in the image forming apparatus of the present invention will be described.
[0222]
Even during normal image formation, the amount of toner remaining after transfer slightly changes, but the amount of toner remaining after transfer increases greatly. (1) When a jam that means paper jam occurs, (2) A3 original When there is toner to be input to the cleaning unit without passing through the A4 transfer paper while creating a toner image, (3) When the transfer efficiency decreases due to changes in the paper thickness or environment and the amount of residual toner increases There is.
[0223]
Here, as an example of the operation after the occurrence of an abnormality, a timing chart after the occurrence of a jam is shown in FIG.
[0224]
When a jam occurs, a detection device (not shown) operates to stop the machine, and the power is turned off. In this case, the machine power is turned on again by removing the transfer paper from the jam occurrence place and resetting. On the other hand, depending on the location of the jam, when the machine is stopped, the toner image before transfer remains on the photosensitive drum from the developing position to the transfer position or from the developing position to the cleaning position. If the next image forming process starts as it is, the toner image before the transfer enters the cleaning portion, and the cleaning roller 7A has too much toner amount to be completely removed and passes downstream, so that it contacts like the charging roller 3A. If the charging device is used, the charging device is smudged and white streaks appear on the image. Therefore, in order to prevent this, the toner image must be removed from the photosensitive drum 2 before the next image forming step.
[0225]
As shown in the timing chart of FIG. 17, when the machine power is turned on again after the jam, the photosensitive drum 2 starts to rotate, and the cleaning roller 7A removes the toner on the photosensitive drum as described above. Therefore, a voltage of “+300 V” is applied, the static elimination lamp 11 is “ON”, the charging roller 3A is separated, a development bias of “+150 V” is applied, the applied voltage of the transfer roller 6 is “OFF”, and the toner image Is removed. At this time, most of the toner is removed, but a larger amount than usual is left and passes through the cleaning roller 7A. Since the toner that has passed through the cleaning roller 7A is a negative polarity toner after development, it is collected at the development section. When the developing position passes through the cleaning roller 7A (about 1/2 rotation of the photosensitive drum 2), an electric field stronger than usual in the reverse transition process is formed on the cleaning roller 7A by the voltage control means of the cleaning power supply 7G. Such a voltage is applied (for example, -800V). As a result, all of the toner on the cleaning roller 7A holding more toner than normal is reversely transferred onto the photosensitive drum 2 and reattached, so that it can be transferred to the developing unit and collected by the developing roller 5B.
[0226]
Here, the relationship between the amount of toner held on the cleaning roller 7A and the amount of reverse transition must be a stronger electric field as the amount of toner on the cleaning roller 22 increases as shown in FIG. In general, the photosensitive drum 2 is charged by applying a voltage of “450 V to 500 V” and discharging. The photosensitive drum 2 is charged to “−400 V” when a voltage of “−800 V” is applied to the cleaning roller 7A. Therefore, the voltage applied to the cleaning roller 7A can be set to the maximum voltage that can occur, that is, “−800V” even in normal times, but the photosensitive drum 2 is charged to “−400V” at the time of reverse transition. This potential must be neutralized. As a result, electrostatic fatigue occurs in the photosensitive drum 1 and the life is shortened. However, in the image forming apparatus according to the present embodiment, when the toner is reattached on the photosensitive drum 2 immediately after the power supply “ON” after an abnormality such as the occurrence of a jam, the electric field (− Since the applied voltage is controlled so that an electric field (-800 V) stronger than 500 V) is applied to the cleaning roller 7A, the charging of the photosensitive drum 2 is about 0 to 50 V during normal reverse transition, and electrostatic fatigue Can solve the problem.
[0227]
Therefore, in the image forming apparatus of the present embodiment, electrostatic fatigue is minimized, and the life of the photosensitive drum 2 can be extended without deteriorating the toner removal performance even for abnormal input toner at the time of jam.
[0228]
Next, as another control means of the image forming apparatus of the present embodiment, a toner is re-adhered on the photosensitive drum 2 after a lapse of a certain time of image formation stop, and a voltage control means for the cleaning roller 7A at that time is created. The electric field is stronger than the voltage control means in the image. That is, after a certain period of time has elapsed since image formation is stopped, a voltage stronger than the voltage applied to the cleaning roller 7A by the cleaning power supply 7G is applied to the cleaning roller 7A during image formation, so that an electric field stronger than that during normal image formation is applied. Since the toner is reattached on the photosensitive drum 1, even if an abnormal amount of input toner is generated, for example, when an A3 transfer sheet is passed through an A3 document, all the increased toner is generated on the cleaning roller. It can be reattached on the photosensitive drum, transferred to the developing unit, and collected by the developing roller 5. Therefore, the toner removal performance of the cleaning roller can be prevented from being deteriorated, and the life of the photosensitive drum 1 can be prevented from being reduced.
[0229]
Further, as another control means of the image forming apparatus of the present embodiment, the toner is reattached on the photosensitive drum 2 by a voltage control means having a strong electric field different from the normal once per fixed number of sheets. That is, a voltage stronger than the voltage applied to the cleaning roller 7A is applied to the cleaning roller 7A by the cleaning power source 7G during image formation once every fixed number of times, and is applied onto the photosensitive drum 2 with a strong electric field different from normal. Since the toner is reattached, even when the transfer rate decreases due to the paper thickness or environment and the amount of residual toner increases, all the toner on the cleaning roller 7A that has been removed by removing the toner has increased on the photosensitive drum 1. The toner can be reattached to the developing portion, transferred to the developing portion, and collected by the developing roller 5B. Therefore, the toner removal performance of the cleaning roller 7A can be prevented from being deteriorated, and the life of the photoreceptor can be prevented from being shortened.
[0230]
As described above, the cleaning electric field and the electric field for reverse transition are formed by switching the bias voltage to the cleaning roller 7A in the image forming apparatus of the present embodiment. In the reverse transition step, the surface of the photosensitive member may be charged to a reverse polarity by a transfer charger (or a transfer roller or the like) to switch the electric field.
[0232]
In this embodiment, the contact / separation operation of the cleaning roller 7A with respect to the photosensitive drum 2 is performed under the following conditions.
[0233]
First, when the image forming operation is not performed using the photosensitive drum 2, the cleaning roller 7 </ b> A is separated from the photosensitive drum 2.
[0234]
Second, prior to image formation using the photosensitive drum 2, the cleaning roller 7A comes into contact after the photosensitive drum 2 rotates in the opposite direction to that during image formation.
[0235]
Third, the cleaning roller 7A comes into contact with the photosensitive drum 2 before the photosensitive drum 2 starts normal rotation at the start of image formation.
[0236]
Since the present embodiment is configured as described above, its operation is the same as the timing chart shown in FIG. 6, but the toner reattachment to the photosensitive drum 2 with respect to the separation timing of the cleaning roller 7A. Later, as shown in FIG. 19, the application of the voltage for causing the toner to reattach to the photosensitive drum 2 from the cleaning roller 7A may be completed at the same time. In this case, the switch H in the power source 7G included in the cleaning device 7 is held in a neutral state, and the application of the voltage for redeposition of the toner is stopped.
[0237]
At the same time as the reattachment of the toner is completed, the cleaning roller 7A is separated from the photosensitive drum 2, thereby eliminating the electrostatic influence on the photosensitive drum 2 and temporarily leaving the toner on the cleaning roller 7A. In this case, it is possible to prevent the toner from rubbing on and adhere to the photosensitive drum 2 to prevent the background of the photosensitive drum 2 from being stained.
[0238]
Furthermore, FIG. 20 shows a modification of the voltage application state to the cleaning roller 7A. In this example, when the suction of the residual toner from the photosensitive drum 2 by the rotation of the cleaning roller 7A is completed, The polarity of the voltage applied to the cleaning roller 7A is reversed and set from “−500V” to “+ 300V”. In the cleaning roller 7A in this case, the timing of leaving the photosensitive drum 2 after the polarity conversion for the toner reattachment is completed, as in the case shown in FIG. As described above, when the cleaning roller 7A is separated from the photosensitive drum 2 after the toner redeposition processing is completed, the toner reattached to the toner redeposition region on the photosensitive drum 2. Even when a part of the toner is accidentally attached to the image area on the photosensitive drum 2, the toner can be sucked to the cleaning roller 7A to prevent background stains in the image area.
[0239]
Further, as shown in FIG. 21, the voltage application for reattaching the toner to the photosensitive drum 2 with respect to the cleaning roller 7A is performed from the image formation by the photosensitive drum 2 to the recovery of the developer, that is, the development from the charging step. In the movement period until the residual toner is collected by the apparatus 5, the toner may be continued from the time when the toner sucked by the cleaning roller 7A is reattached to the photosensitive drum 2 until the end of the movement of the photosensitive drum 2. Is possible. In this case, the separation timing of the cleaning roller 7A can be set during the duration. As a result, the polarity of the charged potential in the image area is negativeized until the cleaning roller 7A is separated from the photosensitive drum 2. This is because when the photosensitive layer of the photosensitive drum 2 is made of an organic material such as OPC, the negative charge tendency has a large charge removal effect due to the light discharge in order to prevent the light discharge effect by the charge removal device 11 from being lowered. This is because. Therefore, the charge removal by the light discharge is performed efficiently, and the charging device 3 can perform uniform charging at the next image formation.
[0240]
By the way, normally, when the toner remaining on the photosensitive drum 2 is sucked by the cleaning roller 7A, the cleaning is performed with a movement speed approximately approximate to the movement speed of the photosensitive drum 2 so as not to inhibit frictional charging. When the roller 7A is rotated, as a matter of course, the time until collection by the developing device 5 becomes longer. For this reason, there is a possibility that the waiting time until the next copying operation becomes long and the copying operation cannot be speeded up.
[0241]
Therefore, the moving speed of the cleaning roller 7A is increased with respect to the moving speed of the photosensitive drum 2.
[0242]
FIG. 22 is a timing chart in this case. The peripheral speed corresponding to the moving speed of the cleaning roller 7A is set to a peripheral speed at which 2n rotations (n ≧ 1) can be performed in the reattachment region of the photosensitive drum 2. Yes. As a result, the opportunity for the cleaning roller 7A to face the photosensitive drum 2 increases, so that the time required to reattach the residual toner sucked by the cleaning roller 7A to the photosensitive drum 2 can be shortened.
[0243]
Therefore, as shown in FIG. 23, the time required for reattachment of the toner to the photosensitive drum 2 in the paper feed process period (referred to as a sheet interval in the figure) which is a process used for the next image formation is shortened. Therefore, the time until the second image is formed can be shortened.
[0244]
By the way, at the time of image formation, image formation may be interrupted by accidents, such as a paper jam. In this case, as in the case of starting up or warming up, when the cause of the interruption is eliminated and the image forming apparatus is restarted, the image area of the photosensitive drum 2 corresponds to before reaching the transfer device 6 or before reaching the cleaning device 7. There is a case. When the apparatus is restarted in such a state, the toner adhering to the surface of the photosensitive drum 2 is removed for initialization.
[0245]
However, when the cleaning device 7 tries to remove the toner remaining on the photosensitive drum 2, the toner that has not been transferred due to the interruption is included. The removal amount may be larger than in the case of a normal cleaning process. Therefore, when the toner sucked from the photosensitive drum 2 by the cleaning roller 7A is reattached to the photosensitive drum 2, as shown in FIG. 18, the toner applied to the photosensitive drum 2 is re-applied according to the bias voltage. A high voltage is required to change the deposition rate and ensure re-deposition.
[0246]
When the toner is reattached to the photosensitive drum 2 using a bias due to a high voltage, the residual potential on the photosensitive drum 2 is also increased, and the static elimination potential is increased accordingly. The static elimination potential in this case is the amount of light emitted by the static elimination device 11. Therefore, in the photosensitive drum 2, electrostatic fatigue due to the application of a high voltage for attracting the toner to the cleaning roller 7A and the reattachment of the toner to the photosensitive drum 2, and repeated static elimination becomes significant. The life of the body drum 2 may be shortened.
[0247]
Therefore, in another embodiment of the present invention, as shown in FIG. 24, the time required for reattachment to the photosensitive drum 2 is increased without increasing the voltage applied to the cleaning roller 7A. I try to reduce electrostatic fatigue.
[0248]
FIG. 24 is a timing chart for restarting when a paper jam (jam) occurs. When a jam occurs, each apparatus related to image formation stops. For this reason, the bias in the charging device and other devices using the bias is stopped.
[0249]
When the jammed paper, which is the cause of the interruption in the apparatus, is removed and the apparatus door is closed, the photosensitive drum 2 resumes rotation, and the developing apparatus 5 except for the charging apparatus 3 performs photosensitive operation. A bias voltage having a polarity for collecting the toner on the body drum 2 is used. In the cleaning device 7, the bias voltage having a polarity necessary for sucking the residual toner from the photoreceptor drum 2 and the sucked toner are used as the photoreceptor. A bias voltage having a polarity necessary for reattachment to the drum 2 is applied. As with the above-described embodiment, the charge removal apparatus 11 performs a charge removal process from the time when the photosensitive drum 2 starts to resume rotation until the image can be formed.
[0250]
In FIG. 24, when the rotation of the photosensitive drum 2 is resumed, residual toner is sucked from the image area on the photosensitive drum 2 by the cleaning device, and the image area of the photosensitive drum 2 is moved to the cleaning roller 7A. When the amount corresponding to one rotation or more is moved, toner reattachment from the cleaning device 7 toward the photosensitive drum 2 is executed. The time required for toner re-adhesion is set longer than the time required for re-adhesion performed during normal image formation. In this embodiment, the time required for re-adhesion is twice as long as an integral multiple of the normal re-adhesion time. Set to time. The bias voltage applied to the cleaning device 7 in this case is selected to be the same value as the applied voltage at the time of image formation that is normally executed.
[0251]
In the present embodiment, the same bias voltage as that used when the toner is reattached to the photosensitive drum 2 in the cleaning process at the time of image formation, which is normally executed, can be used as the bias voltage required for toner reattachment to the photosensitive drum 2. Therefore, the electrostatic fatigue of the photosensitive drum 2 is not increased, and all of the toner sucked by the cleaning roller 7A can be reattached to the photosensitive drum 2.
[0252]
FIG. 25 illustrates the case where the sheet interval is set in order to form an image on a plurality of (two) transfer sheets, and the residual toner is attracted to the cleaning roller 7A and the toner is reattached to the photosensitive drum 2. 6 is a timing chart showing an operation state of each device when a jam occurs in the second image area.
[0253]
In FIG. 25, since the above-described toner collection and initialization of the photosensitive drum 2 are respectively performed, description will be given in the drawing, and detailed description will be omitted.
[0254]
By the way, a photoconductor used in an image forming apparatus may cause a filming phenomenon in which toner accumulates on the photosensitive layer. In this filming, if toner accumulates more than necessary, charging efficiency and formation of an electrostatic latent image may be hindered, which may affect the life of the photosensitive member and can be suppressed. is necessary.
[0255]
Therefore, in this embodiment, the occurrence of filming is also prevented.
[0256]
In the present embodiment, the rotation speed of the cleaning roller 7A is set to be higher than the rotation speed at the time of the suction of the toner from the photosensitive drum 2 and the reattachment of the toner to the photosensitive drum 2 that is normally performed only for a certain period. By setting a high speed, the friction force between the surface of the photosensitive drum 2 is increased and the accumulated toner is removed.
[0257]
In FIG. 26, the bias voltage applied to the cleaning roller 7A for attracting and reattaching the toner to the photosensitive drum 2, which is the initialization of the photosensitive drum 2 performed after the power of the image forming apparatus is turned on. When the polarity reversal is completed, the rotational speed of the cleaning roller 7A is increased and rotated once. As a result, the friction force between the photosensitive drum 2 and the toner accumulated on the surface of the photosensitive drum 2 is scraped off.
[0258]
Next, a modification of the present embodiment will be described with reference to FIG.
[0259]
The example shown in FIG. 27 has a feature in the contact / separation relationship between the photosensitive drum 2 and the cleaning roller 7A that can contact / separate the photoreceptor drum 2.
[0260]
In FIG. 27, when the print button is turned on, the photosensitive drum 2 rotates in the direction opposite to the rotation direction at the time of image formation (indicated by “reverse rotation” in FIG. 27). The reverse rotation amount in this case is set to an amount corresponding to the length of the nip portion or more shown in FIG. 5 along the circumferential direction of the photosensitive drum 2, so that the next image formation is performed. Therefore, when the photosensitive drum 2 is rotated forward, the nip portion can make the entire region face the cleaning roller 7A, so that the toner remaining on the surface of the photosensitive drum 2 is forward-rotated. All of them are removed when passing the position of the cleaning roller 7A.
[0261]
The cleaning roller 7 </ b> A is maintained in a state of being separated from the photosensitive drum 2 when image formation using the photosensitive drum 2 is not performed and image formation is not performed. Since this state includes the above-described reverse rotation of the photosensitive drum 2, as shown in FIG. 27, the photosensitive drum 2 is separated from the photosensitive drum 2, but is synchronized with the time when the normal rotation of the photosensitive drum 2 is started. The cleaning roller 7A comes into contact with the photosensitive drum 2 before each bias is turned on. Thus, when the photosensitive drum 2 starts to rotate in the forward rotation direction from the stopped state, the toner remaining in the nip portion is scraped off by the cleaning roller 7A.
[0262]
Further, as shown in FIG. 27, the separation timing of the cleaning roller 7A from the photosensitive drum 2 is a fixed time (after the image formation executed by the rotation of the photosensitive drum 2 in the normal rotation direction is completed). In the figure, it is a time point when a period indicated by a symbol T) has elapsed. As a result, the photosensitive drum 2 can be maintained in a stopped state in a state where almost all of the toner remaining on the photosensitive drum 2 is scraped off. At the same time, the cleaning roller 7A is also separated from the photosensitive drum 2, so that the surface state of the photosensitive drum 2 is not changed.
[0263]
By setting the contact / separation operation of the cleaning roller 7A with respect to the photosensitive drum 2 as described above, almost all of the toner remaining on the surface of the photosensitive drum 2 is eliminated by facing the cleaning roller 7A. In addition, when the image formation is not performed, the cleaning roller 7A is kept away from the photosensitive drum 2, so that when the photosensitive drum 2 rotates forward for the next image formation, the surface of the cleaning roller 7A is not moved. A state in which no toner is present can be obtained. This prevents the toner from adhering to the charging roller 3A that contacts the photosensitive drum 2 for the next image formation, so that a part of the peripheral surface of the charging roller 3A is uniformly charged by the toner adhering. Can be prevented.
[0264]
It should be noted that the present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist. For example, in the embodiment shown in FIG. 1, when the collected toner adsorbed on the cleaning roller 7A is reused, a negative polarity bias voltage is applied to the cleaning roller 7A to collect it from the cleaning roller 7A toward the photosensitive drum 2. In place of this, instead of this, a positive polarity bias voltage is applied to the transfer roller 6 to charge the surface of the photosensitive drum 2, and the recovered toner attached to the cleaning roller 7A is attached to the photosensitive drum 2. You may do it.
[0265]
Furthermore, the cleaning roller 7A may be formed of a foamable member that is an elastic body, and the bubble diameter on the surface may be 50 μm or less and smaller than the bubble diameter inside. With such a configuration, residual toner is prevented from entering the foamed molded product during cleaning.
[0266]
Further, instead of the photosensitive drum 2, an image carrier may be configured by a belt-shaped photosensitive member. The image carrier may be used for a color copying machine. In this case, an intermediate transfer member such as an intermediate transfer belt can be used as the configuration of the image carrier.
[0267]
In addition to changing the direction of the electric field by switching the polarity of the bias voltage to the cleaning roller, the polarity of the bias voltage is made constant, and the direction of the electric field is set by setting the polarity and the surface potential on the image carrier side. You may make it switch. In this case, the polarity and surface potential on the image carrier side can be set by using a transfer device.
[0268]
【The invention's effect】
As described above, according to the first aspect of the invention, during recording, the cleaning roller rotates together with the image carrier, and the toner remaining on the image carrier after the transfer is rubbed between them. The toner is charged to the same polarity and is electrostatically adsorbed by the cleaning member, and at the same time, a voltage is applied to the cleaning member by the voltage applying means, and the residual toner on the image carrier charged to the same polarity is applied to the cleaning member. The image carrier surface is adsorbed and the surface of the image carrier is cleaned. Even if +/- bipolar toner remains on the image carrier, all of the toner is completely adsorbed by a simple configuration. Can be cleaned.
[0269]
According to the second aspect of the present invention, when the collected toner adsorbed by the cleaning member is reused, the voltage applying means applies a voltage having a polarity opposite to that at the time of adsorption to the cleaning member and adheres to the cleaning member. The toner that has been attached is reattached to a region other than the region where the next image is formed, and the reattached toner is recovered by being directed back to the developing device side by the voltage of the adsorbable polarity applied to the developing device. Therefore, it is possible to reliably reuse the collected toner.
[0270]
According to the third aspect of the present invention, when the collected toner adsorbed by the cleaning member is reused, the surface of the image carrier is charged by the transfer device, and the toner adsorbed by the cleaning member is used for the next image formation. The toner is reattached to a region other than the region where the toner is applied, and the reattached toner is recovered by adsorbing the toner toward the developing device using the polarity of the voltage applied to the developing device. The toner can be reliably reused.
[0271]
Claim 4And 5According to the described invention, even if a part of the residual toner sucked and held by the cleaning member adheres by reversing the polarity to the polarity opposite to the polarity necessary for holding the suction, By switching the direction, the toner is transferred onto the image carrier, so that all of the toner remaining in the image area on the image carrier can be completely collected by the developing device. Can be reused.
[0273]
Claim6According to the described invention, even when the cleaning member moves in the forward direction and the moving direction of the image carrier, the critical hardness with the least wear of the image carrier is obtained and the frictional charging of the toner is most effectively performed. The polarity of the toner sucked by the cleaning member can be made uniform even if the nip area where the critical pressure and the rubbing speed are obtained is reduced, and the image area of the image carrier can be obtained by the suction bias applied to the cleaning member. Therefore, it is possible to reduce the nip area of the cleaning member and suppress the increase in size of the apparatus including the cleaning member.
[0274]
Claim7According to the described invention, the cleaning member is moved in the direction opposite to the moving direction of the image carrier to obtain the rubbing state necessary for the frictional charging of the toner. By making it possible to easily uniformize the polarity of the toner, it is possible to reduce the size of the apparatus including the cleaning member by reducing the nip area.
[0276]
Claim8According to the invention described above, it is possible to optimally set the electric field strength by the plurality of voltage control means according to the amount of toner adsorbed and held on the cleaning roller, and the toner is surely formed on the photosensitive member. Since the toner can be reattached and can be transferred to the developing unit and collected, the toner removal performance can be prevented from being deteriorated and the life of the image carrier can be prevented from being reduced.
[0277]
Claim9According to the described invention, the voltage control means for forming an electric field so that the developed toner is directed to the cleaning roller is operated, and then the toner on the cleaning roller is reattached on the photosensitive member, and the voltage control means at that time Since the toner is reattached on the photosensitive member by the voltage control means having a stronger electric field than the voltage control means during image formation, it is increased and held on the cleaning roller after the jam to remove the toner having a large M / A after development. All of the toner thus deposited can be re-adhered on the photosensitive member, and can be transferred to the developing unit and collected. As a result, it is possible to prevent the deterioration of the toner removal performance and the life reduction of the image carrier.
[0278]
Claim10According to the described invention, even when an abnormal amount of input toner is generated, for example, when an A3 transfer sheet is passed through an A3 original, all the increased toner is reattached on the photosensitive member. Can be transferred to the developing unit and collected. As a result, it is possible to prevent the deterioration of the toner removal performance and the life reduction of the image carrier.
[0279]
Claim11According to the described invention, the transfer rate decreases due to the paper thickness, environment, etc., the amount of residual toner increases, and the toner on the cleaning roller increased by removing the toner can be reattached to the photoreceptor. It can be transferred to the developing unit and collected. This also makes it possible to prevent the deterioration of the toner removal performance and the life reduction of the image carrier.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a perspective view showing a configuration of a charging device used in the image forming apparatus shown in FIG.
3 is a perspective view showing a configuration of a cleaning device used in the image forming apparatus shown in FIG. 1. FIG.
4 is a schematic diagram for explaining a state of toner remaining on an image carrier after transfer in the image forming apparatus shown in FIG. 1; FIG.
5 is a schematic diagram for explaining the state of toner remaining on the image carrier when facing the cleaning device in the image forming apparatus shown in FIG. 1; FIG.
6 is a timing chart for explaining an operation in the image forming apparatus shown in FIG.
7 is a timing chart for explaining another operation in the image forming apparatus shown in FIG. 1; FIG.
8 is a timing chart for explaining still another operation in the image forming apparatus shown in FIG.
FIG. 9 is a timing chart for explaining another operation in the image forming apparatus shown in FIG. 1;
10 is a timing chart for explaining still another operation in the image forming apparatus shown in FIG.
11 is a timing chart for explaining a modified example of the operation in the image forming apparatus shown in FIG.
12 is a cross-sectional view showing a modification of the main part of the image forming apparatus shown in FIG.
13 is a diagram for explaining one of the characteristics of the cleaning roller used in the cleaning device shown in FIG. 3; FIG.
14 is a diagram for explaining another characteristic of the cleaning roller used in the cleaning device shown in FIG. 3; FIG.
15 is a schematic diagram for explaining a facing relationship between a cleaning roller and an image carrier in the cleaning device in the image forming apparatus shown in FIG.
FIG. 16 is a schematic diagram for explaining a problem in a facing relationship between the cleaning roller and the image carrier in the cleaning device in the image forming apparatus.
17 is a timing chart showing an operation after occurrence of a jam in the image forming apparatus shown in FIG.
FIG. 18 is a graph showing the relationship between the amount of toner held on the cleaning roller and the amount of redeposition on the photosensitive member using the applied voltage as a parameter.
FIG. 19 is a timing chart for explaining still another operation in the image forming apparatus shown in FIG. 1;
20 is a timing chart for explaining another operation in the image forming apparatus shown in FIG. 1; FIG.
FIG. 21 is a timing chart for explaining another operation in the image forming apparatus shown in FIG. 1;
FIG. 22 is a timing chart for explaining yet another operation in the image forming apparatus shown in FIG. 1;
FIG. 23 is a timing chart for explaining a modification of the operation in the image forming apparatus shown in FIG. 1;
24 is a timing chart for explaining still another modification of the operation of the image forming apparatus shown in FIG.
FIG. 25 is a timing chart for explaining another modified example of the operation in the image forming apparatus shown in FIG. 1;
FIG. 26 is a timing chart for explaining still another modification example of the operation of the image forming apparatus shown in FIG. 1;
FIG. 27 is a timing chart for explaining still another embodiment in the image forming apparatus shown in FIG. 1;
FIG. 28 is a schematic diagram for explaining one of the conventional examples of the image forming apparatus.
FIG. 29 is a schematic diagram for explaining another conventional example of the image forming apparatus.
[Explanation of symbols]
1 Image forming device
2 Photosensitive drum as an image carrier
3 Charging device
5 Development device
5E power supply
6 Transfer device
7 Cleaning device
7A Cleaning roller
7G power supply

Claims (11)

An image carrier, and a cleaning member made of a rotatable conductive roller arranged in a state of being pressed against the surface of the image carrier,
During one image forming process on the image carrier, an electric field in one direction is applied to adsorb and hold the residual toner adhering to the surface of the image carrier on the cleaning member, and then the direction of the electric field is changed. Then, the toner held by suction is reattached to a region on the image carrier that does not affect the next image formation, and transferred to the developing unit used in the image forming process, and transferred to the developing unit. In an image forming apparatus that electrostatically collects toner,
The cleaning member is disposed in contact with the image carrier, rotates a image bearing member and the speed difference, the residual toner adhering to the image carrier after the transfer at the nip portion between the image bearing member friction charged, and the cleaning roller for charging the toner to the same polarity,
Voltage applying means for applying a voltage to the cleaning roller and adsorbing the residual toner on the image carrier charged to the same polarity to the cleaning roller;
When the cleaning roller is frictionally charged by forming a nip portion at the contact portion with the image carrier and rubbing the residual toner, the cleaning roller can apply a voltage having a polarity opposite to that of the toner charged to the same polarity by the voltage applying means. An image forming apparatus, wherein the polarity of the voltage applied by the voltage applying means is switched when the residual toner is sucked and the sucked residual toner is returned to the image carrier. The image forming apparatus according to claim 1.
In addition to the voltage applying means provided in the cleaning member, the developing device used in the image forming process includes a voltage applying means,
The voltage applying means included in the cleaning member applies a voltage opposite to that collected by the cleaning roller when the toner collected and collected on the cleaning roller is reused. The toner collected by adhesion is reattached to an area other than the area where the next image formation is performed on the image carrier,
An image forming apparatus, wherein the voltage applying means provided in the developing device applies a voltage having a polarity capable of attracting the toner reattached on the image carrier to the developing device. The image forming apparatus according to claim 2.
In addition to the voltage applying means provided in the cleaning member and the voltage applying means provided in the developing device, the transfer device used in the image forming process includes a voltage applying means,
The voltage application means provided in the transfer device applies an opposite voltage to the image carrier when the toner collected and collected on the cleaning roller is reused. By charging the surface of the carrier, the toner attached and collected on the cleaning roller is reattached to a region other than the region where the next image formation is performed on the image carrier,
An image forming apparatus, wherein the voltage applying means provided in the developing device applies a voltage of an electrode capable of adsorbing the toner reattached on the image carrier to the developing device. The image forming apparatus according to claim 1.
The cleaning member first forms an electric field in a direction in which the residual toner can be sucked from the image carrier as a switching order of the electric field direction when the residual toner is reattached on the image carrier. An image forming apparatus, wherein the electric field is set in the order in which the residual toner is transferred onto the image carrier. The image forming apparatus according to claim 4.
In the cleaning member, the voltage of the electric field formed first is opposite to the polarity of the charged charge generated in the toner due to the frictional charging caused by the contact between the cleaning member and the image carrier, and is sucked from the image carrier. An image forming apparatus characterized in that the voltage is set to be higher than a voltage used in the above. The image forming apparatus according to claim 1.
The cleaning member is made of rubber having a hardness of Asuka C20 to 38 degrees, the pressing force against the image carrier is 3 g / cm or more, and the linear velocity ratio with the image carrier is less than 1. An image forming apparatus that is set and moves in a forward direction and a moving direction of the image carrier. The image forming apparatus according to claim 1.
The cleaning member is made of rubber whose hardness is set to 20 to 38 degrees asuka C, and the pressing force against the image carrier is set to 3 g / cm or more, which is opposite to the moving direction of the image carrier. And an image forming apparatus. The image forming apparatus according to claim 4.
The cleaning member includes a plurality of voltage control means for applying a voltage capable of transferring the toner collected and adhered from the image carrier to the image carrier.
2. The image forming apparatus according to claim 1, wherein the plurality of voltage control means have different electric field strengths such that the toner held on the cleaning roller is directed toward the photoconductor. The image forming apparatus according to claim 8.
In order to remove the toner on the photoconductor immediately after the power is turned on or during the warm-up, a voltage control unit is applied to form an electric field so that the developed toner is directed to the cleaning roller, and then the toner on the cleaning roller is transferred to the photoconductor An image forming apparatus, wherein the image forming apparatus is reattached to the top and the voltage control unit at that time forms a stronger electric field than the voltage control unit during image formation. The image forming apparatus according to claim 8.
An image forming apparatus, wherein toner is reattached on a photosensitive member after a certain time has elapsed since image formation is stopped, and the voltage control means at that time forms a stronger electric field than the voltage control means during image formation. The image forming apparatus according to claim 8.
An image forming apparatus wherein toner is reattached on a photosensitive member by a voltage control means having a strong electric field different from normal once per fixed number of sheets.

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